ML19257B245

Forwards Response to NRC 791109 Request for Info Re Fuel Rod Models Used in LOCA ECCS Model.Westinghouse Has Recognized That Heatup Rate Dependence of Burst Was Not Properly Considered

ML19257B245
Person / Time
Site:	Farley
Issue date:	01/10/1980
From:	Clayton F ALABAMA POWER CO.
To:	Schwencer A Office of Nuclear Reactor Regulation
References
NUDOCS 8001150406
Download: ML19257B245 (6)

Text

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Alabama Power Company 600 North 18th Street Post Office Box 2641 Birmingham. Alabama 35291 Telephone 205 323-5341 L';; owe'eTe';sni AlabamaPower b

the southem dectrc system January 10, 1980 Docket No. 50-348 Director Office of Nuclear Reactor Regulation U. S. Nuclear Regulatory Commission Washington, D.C. 20555 Attn: Mr. A. Schwencer Gentlemen:

J. M. FARLEY NUCLEAR PLANT FUEL ROD BURST MODEL Your letter dated November 9, 1979 requesting information regarding the fuel rod models used in the J. M. Farley Nuclear Plant Loss of Coolant Accident (LOCA) ECCS model, was not received by Alabama Power Company. A copy was obtained from Southern Company Services, Inc. on December 28, 1979 and Alabama Power Company's response is enclosed.

Since the original request, Westinghouse recognized a potential dis-crepancy in that the heatup rate dependence of burst was not properly con-sid ered. Evaluation of the impact of the heatup rate dependence on fuel rod burst was presented to the NRC in Westinghouse's letter NS-TMA-2163 dated November 16, 1979.

The information provided in the attachment contains response to the original request, improvement to the heatup rate prior to burst definition and the use of credit from improved analytical and modeling techniques to offset the ef fect of the new NRC model to meet the acceptance criteria for 10CFR50.46 with an FQ (heat flux hot channel factor) of 2.32.

Should you have any questions, please advise.

Yours truly,

,

. .t - -.

F. L. Clayton, Jr.

FLCJr/TNE:bhj [ 039 S

Enclosure /

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f 8001150 46G

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Office of Nuclear Reactor Regulation Page 2 July 10, 1980 cc: Mr. R. A. Thomas Mr. G. F. Trowbridge 1749 186

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ATTACHMENT A. Evaluation of the potential impact of using fuel rod models presented in draft NUREG-0630 on the Loss of Coolant Accident (LOCA) analysis for Joseph M. Farley Unit 1.

This evaluation is based on the limiting break LOCA analysis identified as follows:

BREAK TYPE - DOUBLE ENDED COLD LEG GUILLOTINE BREAK DISCHARGE COEFFICIENT 0.4 WESTINGHOUSE ECCS EVALUATION MODEL VEPSION Modified

• February,1978

• The fuel rod burst model was modified to factor in heatup rate dependence as documented in WCAP-8970-P-A, " Westinghouse Emergency Core Cooling System Small Break, October 1975 bbdel". Fuel rod burst curves used in this analysis represented clad heatup rates of 10 Deg. F/sec for the Hot Rod and 10 Deg. F/sec for the Average Hot Assembly Rod.

CORE PEAKING FACTOR 2.32 HOT R0D MAXIMUM TEMPERATURE CALCULATED FOR THE BURST REGION OF THE CLAD - 1974 0F = PCT B ELEVATION - 6. 0 Feet.

HOT R0D MAXIMUM TEMPERATURE CALCULATED FOR A NON-RUPTURED REGION OF THE CLAD - 2200 F = PCTN ELEVATION - 7.5 Feet CLAD STRAIN DURING BLOWDOWN AT THIS ELEVATION 0.9 Percent MAXIMUM CLAD STRAIN AT THIS ELEVATION 3.4 Percent Maximum temperature for this node occurs when the core reflood rate is less than 1.0 inch per second and reflood heat transfer is based on the Steam Cooling calculation.

AVERAGE HOT ASSEMBLY R0D BURST ELEVATION - 6.0 Feet HOT ASSEMBLY BLOCKAGE CALCULATED - 47.0 Percent

1. BURST N0DE The maximum potential impact on the ruptured clad node is expressed in letter NS-TMA-2174 in terms of the change in the peaking factor limit (F )Q required to maintain a peak clad tem-perature (PCT) of 22000F and in terms of a change in PCT at a constant FQ. Since the clad water reaction rate increases sig-nificantly at tenperatures above 22000F, individual effects (such as aPCT due to changes in several fuel rod models) indicated here may not accurately apply over large ranges, but a simultaneous 1749 187

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change in FQ which causes the PCT to remain in the neighborhood of 22000F justifies use of this evaluation procedure.

From NS-TMA-2174:

For the Burst Node of the clad:

-

0.01 AFQ s 1500F BURST N0DE APCT

- Use of the NRC burst model could require an FQ reduction of 0.015

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The maximum estimated impact of using the NRC strain model is a required FQ reduction of 0.03.

Therefore, the maximum penalty for the Hot Rod burst node is:

aPCT j =

(.015 + .03) (1500F/.01) = 6750F Margin to the 22000F limit is:

=

APCT2 22000F - PCTB = 2260F The FQ reduction required to maintain the 22000F clad temperature limit is:

AFQ B = (aPCT) - APCT2 )

(~ 0F)

= (675 - 226) ( 0)

= 0.03

2. NON-BURST N0DE The maximum temperature calculated for a non-burst section of clad typically occurs at an elevation above the core mid-plane during the core reflood phase of the LOCA transient. The poten-tial impact on that maximum clad temperature of using the NRC fuel rod models can be estimated by examining two aspects of the analyses. The first aspect is the change in pellet-clad gap conductance resulting from a difference in clad strain at the non-burst maximum clad temperature node elevation. Note that clad strain all along the fuel rod stops after clad burst occurs and use of a different clad burst model can change the time at which burst is calculated. Three sets of LOCA analysis results were studied to establish an acceptable sensitivity to apply generically in this evaluation. The possible PCT increase resulting from a change in strain (in the Hot Rod) is +200F per percent decrease in strain at the maximum clad temperature locations.

Since the clad strain calculated during the reactor coolant system blowdown phase of the accident is not changed by the use of NRC fuel rod models, the maximum decrease in alad strain that must be considered here is the difference bety.en tne " maximum clad strain" and the

" clad strain during blowdown" indica'.ed above.

1749 188

.. Therefore:

APCT3* ( strain) (IMX STRAIN - BLOWDOWN STRAIN)

=

(201) (.034 .009)

= 0 50 F The second aspect of the analysis that can increase PCT is the flow blockage calculated. Since the greatest value of blockage indicated by the NRC blockage model is 75 percent, the maximum PCT increase can be estimated by assuming that the current level of blockage in the analysis (indicated above) is raised to 75 percent and then applying an appropriate sensitivity formula shown in NS-TIM-2174.

Therefore:

=

APCT4 1.250F (50 - PERCENT CURRENT BLOCKAGE)

+ 2.360F (75-50)

=

1.25 (50 - 47) + 2.36 (75-50)

= U 63 F If PCTN occurs when the core reflood node is greater than 1.0 inch per second APCT, = 0. The total potential PCT increase for the non-burst node is then aPCTS = APCT3 + APCT4

= 50 + 63 = ll30F Margin to the 2200 0 F limit is APCT6

= 22000 F - APCTg = 0 The FQ reduction required to maintain this 22000F clad temperature limit is (from NS-Ti%-2174).

'

=

aFQ N (aPCTS - APCT 6 ) (l F PCT) aFQ = 0.11 N

The peaking factor reduction required to maintain the 22000F clad temperature limit is therefore the greater of AFQ Band aFQN '

or: a FQ PENALTY " 0*II 1749 189 B. The effect on LOCA analysis results of using improved analytical and modeling techniques (which are currently approved for use in the Upper Head Injection plant LOCA analyses) in the reactor coolant system blowdown calculation (SATAN computer code) has been quantified

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-4 via an analysis which has recently been submitted to the NRC for review. Recognizing that review of that analysis is not yet complete and that the benefits associated with these model improve-ments can change for other plant designs, the NRC has established a credit that is acceptable for this interim period to help offset penalties resulting from application of the NRC fuel rot models.

That credit for two, three and four loop plants is an increase in the LOCA peaking factor limit of 0.12, 0.15, and 0.20 respectively.

C. The peaking factor limit adjustment required to justify plant operation for this interim period is determined as the appropriate AFQ credit identified in Section (B) above, minus the a FQ calculated in Section (A) above (but not greater than zero[ENALU FQ ADJUSTMENT = 0.15 - 0.11

= 0 1749 190